Extrusion head for producing yarns from a material which has been heated to form a paste

ABSTRACT

An extrusion head (14) for producing yarn from a heat-plasticized material, including at least one body (16) defining a chamber (15) for distributing plasticized material over a plate (38) having extrusion openings formed therein. The chamber is supplied by an upper side channel (19) and comprises a downwardly decreasing cross-section of downward flow over at least a portion (24) of the vertical length of the chamber. This decrease is arranged to generate compressive and shear stresses over time in the plasticized material between the side supply channel (19) and the bottom of the chamber (27), said stresses being respectively substantially the same regardless of the path taken by said plasticized material.

BACKGROUND OF THE INVENTION

The present invention relates to extrusion heads for producing yarnsfrom a thermoplastic material which is heated to form a paste, of thetype comprising at least one body defining a pasty material distributionchamber above a horizontal plate perforated with extrusion apertures,the chamber being supplied with pasty material via at least one upperside feed duct extended about an axis in its terminal section connectingwith the chamber.

A particularly important, although not exclusive, application of theinvention is in the field of the manufacture of synthetic yarns frommolten polymer.

Extrusion heads for producing synthetic yarns are already known. Theycomprise a body having a distribution zone for the pasty material and anextrusion chamber provided at its base with a spinning plate perforatedwith holes from which continuous filaments are formed. These filamentsare gathered together so as to produce one or a more yarns.

The holes provided in the spinning plate can be distributed over arectangular, triangular or annular surface.

In general the known extrusion heads further comprise a central moltenpolymer feed duct disposed along the axis of the extrusion head and ofthe yarn(s) produced.

In this type of extrusion head it is difficult, or even impossible, tointroduce a central filiform component or core into the bundle ofextruded synthetic filaments.

An extrusion head is also known (U.S. Pat. No. 3,307,216) which allows abody to be introduced into the bundle of filaments produced. A head ofthis type comprises a cylindrical body defining an annular chamber fordistributing the pasty material above a perforated plate. The chamber issupplied with pasty material via an upper lateral feed duct. The bodycomprises a central cylindrical recess into which it is possible tointroduce a component which is to be incorporated in the bundle offilaments which surround the latter after extrusion.

However, a head of this type is not without disadvantages either.

Irrespective of the path which the product takes between theintroduction channel and the plate, this type of head does not allow forthe presence of a pasty product of homogeneous viscosity at the plateperforated with holes through which the extruded filaments emerge, socreating differences in quality and durability in the filaments ofextruded material produced.

SUMMARY OF THE INVENTION

The present invention aims to provide an extrusion head for producingyarns from a material which is heated to form a paste which meets thepractical requirements better than those known hitherto, in particularin that it has a lateral pasty product supply, which in particularenables a central component to be introduced into the bundle of extrudedfilaments, whilst ensuring large-scale homogeneity in quality anddurability in the extruded yarns produced, in a manner which is simpleto perform and at low cost.

To this end, the present invention in particular proposes an extrusionhead for producing yarns from a material which is heated to form apaste, of the type described above, characterized in that thedistribution chamber, in the horizontal plane, has a section throughwhich the pasty material passes downwards and which gradually decreasesover at least part of the height of the chamber, in the directiontowards the bottom of the feed duct, this decrease being provided so asto create over time substantially identical pressure and shearingstresses on the pasty material, between the lateral feed duct and thebottom of the chamber respectively irrespective of the path the saidpasty material takes when it flows out of the lateral feed duct at thebottom of the said chamber.

In addition, in advantageous embodiments, various of the followingarrangements are possible, either singly or in combination:

the chamber has a lower area in the form of a slot having a verticalsection which decreases gradually in the direction away from the lateralfeed duct;

if the gap between the walls in a given horizontal plane is designatedby the term "clearance" (H), the lower slot-like area is annular and hascylindrical vertical lateral walls with a constant clearance (H) and aheight (Y) which is measured relative to the horizontal plane delimitingthe bottom of the lower part of the chamber (or relative to the plate,at an approximately constant height), decreasing gradually in thedirection away from the lateral feed duct;

the lower slot-like area has cylindrical vertical lateral walls with agap (H) and a height (Y) relative to the plane delimiting the bottom ofthe chamber, both of which decrease gradually in the direction away fromthe lateral feed duct;

the chamber comprises an upper area in the form of a chute of which thecross-section (s) decreases gradually in the direction away from theinlet aperture of the lateral feed duct, which leads into the saidchamber;

the head further comprises an annular extrusion chamber having aconstant cross-section which, for example, widens conically downwards(in the form of an inverted trapezoid), located above the extrusionplate, in the extension of the distribution chamber;

if R (1) designates the hydraulic radius of the chute, if necessarydefined by the equivalent hydraulic diameter of a section of the chuteby the formula:

    D.sub.3 =4. surface area/perimeter,

the hydraulic radius [R(1)] of the chute and the height [Y(1)] of theslot measured at a distance l from the axis of the lateral feed duct,along the axis of the chute, are determined by the following formulae:

    R (1)=R.sub.0 (1/L).sup.1/3

    Y (1)=Y.sub.0 (1/L).sup.2/3

in which:

R₀ : hydraulic radius of the chute at right angles to the axis of thefeed duct;

L: length of the slot measured from the axis of the feed duct;

Y₀ : maximum height of the slot at right angles to the axis of the feedduct;

R₀ =K. (H², L)^(1/3) and Y₀ =K'. (H².L)^(1/3), K and K' being constants;

K is substantially 0.607 and K' 2.3398;

the extrusion head comprises two distribution chamber sections which aresymmetrical relative to the vertical plane passing through the feed ductaxis;

the cross-section of the chute in the upper area is circular,semi-circular, square or rectangular;

the horizontal section of the lower area of the distribution chamber isO-, C- or U-shaped, the ends of the branches of the C or U being spacedapart to a greater or lesser extent;

the head has a plurality of identical bodies each supplied via arespective lateral feed duct located at the top of the said bodies;

the bodies are distributed about a central recess or hollow core;

the head comprises a cylindrical hollow punch which passes through itfrom one side to the other, the chamber wrapping around the said punch;

the lower area of the chamber opens into an annular extrusion chamberprovided at the bottom, above the plate perforated with extrusionapertures, with an additional homogenizing grid consisting, for example,of a perforated annular plate which is used to improve the homogeneityof the velocities of the pasty material before it is extruded throughthe said plate;

the head comprises cartridge-type heating means (cylindrical heatingelement placed in the and/or around the head body) which may or may notbe removable and may or may not enable a plurality of independent areas,which may be separately controlled, to be defined;

the head comprises means which heat by heat-transfer fluid or by acylindrical electrical resistor.

The invention also relates to an extrusion head for producing yarns frommolten synthetic material comprising at least one body defining achamber for distributing the molten synthetic material above ahorizontal plate perforated with extrusion apertures, the said chamberbeing supplied with synthetic material via at least one upper lateralfeed duct, characterized in that the chamber comprises:

an upper area in the form of a chute of which the cross-section (s)decreases gradually in the direction away from the inlet aperture of thelateral feed duct which leads into the said chamber; and

an annular lower area having cylindrical, vertical lateral walls with aconstant clearance (H) and a height (y), relative to the plate, whichdecreases gradually in the direction away from the said inlet aperture.

Advantageously the chamber is symmetrical relative to the medianvertical plane of the feed duct. The invention will be better understoodfrom the following description of particular embodiments given by way ofnon-limiting example.

BRIEF DESCRIPTION OF THE DRAWINGS

The description relates to the attached drawings, in which:

FIG. 1 is a perspective view of a body with an extrusion headdistribution chamber according to one embodiment;

FIG. 2 is a view in vertical section of an extrusion head according tothe embodiment of the invention described in more detail in this case,provided with a distribution chamber of the type as shown in FIG. 1 andcomprising an extrusion chamber and a distribution grid, above theextrusion grid;

FIG. 3A is a view in vertical section along the line IIIA--IIIA in FIG.1, showing in addition an extrusion chamber in the extension towards thebottom of the distribution chamber;

FIG. 3B is a view in section along the lie IIIB--IIIB in FIG. 3A;

FIG. 3C is a view in section along the line IIIC--IIIC in FIG. 3A;

FIG. 3D is a bottom view of FIG. 3A;

FIG. 4 is a schematic lateral view of the distribution chamber in FIG. 1and FIGS. 3A to 3D, indicating the parameters for calculating thevarious sections of the distribution chamber according to thisparticular embodiment of the invention;

FIG. 5 indicates the definition of one of the parameters for calculatingthe dimensions of the chamber shown in FIG. 4;

FIG. 6 is a bottom view of FIG. 4;

FIGS. 7A, 7B, 7C, 7D, and 7E are vertical cross-section profiles ofupper and lower sections of the distribution chamber according toembodiments of the invention;

FIGS. 8A, 8B, 8C and 8D are schematic illustrations in plan view ofembodiments of distribution chambers, according to the invention, whichare symmetrical relative to the vertical plane passing through the feedduct axis;

FIGS. 9A, 9B and 9C are plan views of extrusion heads according to theparticular embodiments of the invention, which are circular or in theform of one or a plurality of circle sections;

FIGS. 10A, 10B and 10C are further embodiments, in plan view, ofextrusion heads according to the invention, comprising a plurality ofbodies;

FIG. 11 is a perspective view of the distribution chamber of a headaccording to a further embodiment of the invention; and

FIG. 12 is a schematic diagram of a device using an extrusion headaccording to the embodiment of the invention described in particular inthis case.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an extrusion head or body member 1 comprising adistribution chamber according to the particular embodiment of theinvention described in this case.

The body 1, for example made of stainless steel or more generally of aheat-conductive material, is a cylindrical with a vertical axis 2pierced from one lateral to the other by a central cylindrical hollowpunch 3 having the same vertical axis.

The body is moulded and defines a distribution chamber 4 which canreceive the molten synthetic material, for example nylon orpolyethylene. The chamber is formed by a recess provided in the bodywhen it is moulded.

A lateral tube 5 for supplying synthetic material and extending about anaxis 6 perpendicular to the vertical axis 2 of the body 1 over at leasta terminal section connecting with the body is provided at the top 7 ofthe body. The chamber is symmetrical relative to the vertical plane 8passing through the axis 6 of the said tube, and wraps around the hollowpunch 3.

The distribution chamber 4 comprises an upper area 9 or chute of whichthe cross-section (s) is circular and decreases gradually in thedirection away from the inlet 10 of the lateral feed duct 5 which leadsinto the chamber. The chute is thus generally crescent-shaped, the cuspsof the crescent closing up on themselves about a transverse plane ofsymmetry inclined relative to the horizontal plane by an angle α.Furthermore, the distribution chamber 4 has an annular cylindrical lowerarea or section 11 having the same vertical axis 2 as the body and awidth or clearance H in the constant horizontal plane and a height (y),measured between the base 12 of the chute 9 and the lower horizontalplane 13 delimiting the bottom or lower part of the distributionchamber, which decreases gradually in the direction away from the inletaperture 10 of the tube 5 in the chamber.

FIG. 2 shows in vertical section an extrusion head 14 according to anembodiment of the invention having a distribution chamber 15 of the typeshown in FIG. 1.

The head 14 comprises a cylindrical body 16, known as the die plate bodymember, about a vertical axis 17, comprising a recess or hollowcylindrical central punch 18 with the same axis 17.

The chamber is supplied laterally with pasty synthetic material via acylindrical pipe 19 with a horizontal axis 20 at the point where thepipe enters the chamber at the top of the body 16.

The distribution chamber 15 has a section for the downwards passage ofthe pasty material (in the direction of the arrow 23) in the horizontalplane which decreases gradually in the downwards direction over at leasta part 24 of the section of the chamber 25 located between thehorizontal plane 26 passing through the lower generating line of theinlet aperture 21 and the lower horizontal plane 27 delimiting thebottom of the distribution chamber or lower part.

More precisely, as shown in FIG. 2, the distribution chamber comprisesan upper crescent-shaped chute 28 of which the cusps 29 join at 30symmetrically relative to the axis of the head 17, opposite the inletaperture 21, and a lower annular area or section 31 with cylindricalwalls, likewise with an axis 17, and having a height (y) which decreasesgradually in the direction away from the said inlet aperture 21, betweentwo values designated h₁ and h₂ in FIG. 2, h₁ being the height betweenthe horizontal planes 26 and 27 and h₂ being the height of the lowerpoint of the chute at 30, still relative to the plane 27. It should benoted that the value of h₂ is 0 in FIG. 1. Similarly, it should be notedthat the height of the section 24 is equal to h₁ -h₂.

The lower area 31 extends the upper chute 28 directly in a verticaldirection, the median vertical cylinder of this lower area 31,equidistant from the walls of the said area, comprising the lowergenerating line of the chute 28.

The lower area 31 of the head 15 opens out at the bottom onto an annularextrusion chamber 32 having a vertical axis 17 and a constant vertical,trapezoidal or isosceles section, which widens downwards at the top 34thereof and is rectangular at the bottom 35.

The head further comprises an annular distribution grid 36, known perse, located below the bottom 35 of the extrusion chamber 32.

This grid is perforated and can in certain cases enable the homogenizingof the speeds and pressures to which the pasty material is subjected asit passes into the head around the punch 18 to be further improved suchthat the viscosity of the pasty material is thoroughly homogeneous.

Depending on the polymer extruded and its degree of purity, a filtrationsystem (not illustrated) might also be used.

For example, the bottom 35 of the extrusion chamber could furthercomprise one or more annular metal filter screens of suitable aperture.

Or, if necessary, a filtration system known per se could be used,comprising porous filter cartridges or a bed of granular material, forexample.

Finally, the head 14 comprises at the bottom 37 an annular spinningplate 38 which is perforated at the center 39 thereof by a cylindricalhole having the same diameter as the hole in the punch 18 and perforatedwith fiber-extrusion holes 40 regularly distributed over the surfacethereof and having a graded diameter.

In the embodiment described above, the cylindrical body 16 is made ofheat-conductive material. Electrical resistors 41 and 42 internally andexternally of the body 16 respectively for heating and/or maintainingthe temperature of the said body by conduction and/or radiation areprovided. They consist for example of cylindrical coils by heatingresistance wires which are supplied with electricity and cooperatecontiguously with the internal and external faces of the cylindricalbody of the head.

A further provision can be the control of the temperature of the bodyand thus of the material which it contains and is being extruded. Thetemperature is regulated by means which heat electrically the resistorscontrolled by means of thermoelectric couples (not illustrated) securedin a regular manner on the body 16 for example.

A heat-insulated protective hood 43 covers the body and the resistorsover their entire outer surface with the exception of the lower facefrom which the extruded filaments emerge.

It will be appreciated that other means for heating the body can also beprovided, for example by circulating a heat-transfer fluid inside and/orin contact with the exterior of the body 16.

In other embodiments the body is made of material which is notheat-conductive. No means for heating the pasty material is thereforeprovided on the head, since the pasty material only remains inside thesaid extrusion head for a limited amount of time and does not vary thetemperature thereof in an obtrusive manner or to a significant degree.

At the top, FIGS. 3A to 3D show in vertical section the body of FIG. 1.When appropriate the same reference numbers as those used in FIG. 1 havetherefore been used in these Figures. The distribution chamber 4 thereinis extended by an annular extrusion chamber 44 having a constanttrapezoidal cross-section which widens at the bottom and of which theupper base 45 has a width H equal to that of the vertical slot of thelower area 11 of the distribution chamber 4.

In this embodiment, the inlet aperture 10 is within the projection inthe vertical plane of the chute 9 (cf. FIG. 3B).

The calculation of the dimensions of the distribution chamber accordingto the invention will now be explained in greater detail.

As generally defined, the distribution chamber according to theinvention has a section for the downwards passage of the pasty materialin the horizontal plane which decreases gradually in the direction awayfrom the lower horizontal plane tangential to the lateral feed ductperpendicular to the head, this decrease being provided so as to createover time substantially identical pressure and shear stresses on thepasty material, irrespective of the path taken by the said pastymaterial when it flows out of the lateral feed duct at the bottom of thechamber.

The calculation of the shapes of the chute and of the slot in theembodiment of the invention described here in particular, like that ofany other shape meeting the above criterion, follows directly from thecalculation of the shape of the known type of annular die plate having awide slot.

It is thus within the scope of the person skilled in the art who willalso take the following assumptions into account:

the incompressibility of the fluid;

the isothermic nature of the fluid (it is accepted that there is noviscous dissipation or heat transfer by conduction);

no interaction in the fluid between the duct and the slot.

The conditions with limits set down by the above definition areexpressed in that the isobars in the fluid pasty material when itdescends downwards are parallel to the slot at the outlet of thedistribution chamber.

Furthermore the inventors hypothesized that it was appropriate to useso-called "representative" viscosities known to the person skilled inthe art.

For laminar and isothermic pressure flow rates there is a location inthe flow duct where the shear velocities encountered for a product of apseudo-plastic nature have a profile identical to that of a Newtonianproduct. "Representative" viscosities of a product of a pseudo-plasticnature can thus be represented simply from poise flows which aretubular, planar, etc.

For this purpose reference is made to the following table:

    ______________________________________                                                    PSEUDO-PLASTIC STRUCTURE                                          GEOMETRY    REPRESENTATIVE VALUE                                              ______________________________________                                        circle                                                                                     ##STR1##                                                         rectangular slot                                                                           ##STR2##                                                         annular slot                                                                               ##STR3##                                                         ______________________________________                                    

The meanings of the parameters used in this table are as follows:

γ : viscosity

Q: flow rate of the pseudo-plastic material passing through the shape inquestion with:

in the case of a cylindrical slot

R: radius of the circle

e₀ : shape factor connected with the viscosity of the product

in the case of a rectangular slot

B: length of the rectangle

H: width of the rectangle

e.sub. : shape factor connected with the viscosity of the product

: *in the case of an annular slot

R_(e) : external radius of the ring

R_(i) : internal radius of the ring

H: width of the ring (H=R_(e) -R_(i))

As an example, a calculation will now be made within the scope of theembodiment described more particularly in this case, using the referencenumbers from FIGS. 4, 5 and 6.

For reasons of symmetry, the chute and the slot are calculated for halfof the distribution chamber.

The following parameters are used:

Q₀ : flow rate over half the distribution chamber

H: constant clearance of the slot 50 forming the lower area

Y₀ : maximum height of the slot, Y₀ =Y(L)

L: length of the outlet slot in the horizontal outlet plane 51 (overhalf the chamber)

l: step of variation over the length L

R₀ : initial radius of the chute 52

dP: pressure drop

γg: representative shearing rate in chute 52

γf: representative shearing rate in slot 50

ηg: representative viscosity in the chute

ηf: representative viscosity in the slot

v: average velocity of the pasty material

θ: angle of revolution of the shape about the axis 53 of the hollowcylindrical punch

: angle between the circumference of the chute and the horizontal planeat the slot (tan =dy/dl).

The following calculations should then be made:

With respect to the section of the chute, assuming that the shearingstress at the wall is not a function of l, it is sufficient to writedown that the shearing rate is then constant, i.e.: ##EQU1##

It then follows that:

    R(1)=R.sub.0.(1/L).sup.1/3                                 (2)

With respect to the calculation of the shape of the slot (lower area ofthe distribution chamber), the procedure is as follows:

Assuming that the output velocity of the pasty material is identicalover the entire width of the distribution chamber, the volume flow ratein the chute should decrease in a linear manner, it follows that:

    Q(l)=Q.sub.0 l/L                                           (3)

For the chute, the average velocity is: ##EQU2##

As regards the slot, the average velocity is calculated by the formula:##EQU3##

This gives a total pressure drop of: ##EQU4##

By adopting the hypothesis according to the invention, i.e. isobarsparallel to the slot, at the outlet of the latter, it follows that:##EQU5##

For the chute, if there is the same shearing rate for each displacement,it follows that:

    ηg=f(1)                                                (10)

As for the slot, H=constant:

    ηf=f(1)                                                (11)

and it follows that: ##EQU6## in which

    R(1)=R.sub.0.(1/L).sup.1/3                                 (2)

which gives ##EQU7##

In this particular case Y₀ is connected with the representativeviscosities of the product. ##EQU8##

The two parameters R₀ and H are freely selected.

In the embodiment described in particular in this case, based on thehypothesis that the product is subject to the same shearing stressirrespective of the path taken, i.e. ##EQU9## in which e₀ =0.815 ande.sub. =0.772 it follows that

    R(1)=0.0607.(H.sup.2.1).sup.1/3                            (21)

    R.sub.0 =R(L)=0.0607.(H.sup.2.L).sup.1/3                   (22)

and

    Y.sub.0 =2.3398.(H.sup.2.L).sup.1/3                        (23)

The shape of the distribution chamber is thus completely independent anduniversal.

In the case of an annular die plate, as shown in FIGS. 4, 5 and 6, Lmerely has to be replaced by πr. and 1 by θ.r which gives:

    Y(θ)=Y.sub.0.(θ/π).sup.2/3                  (24)

    R(θ)=R.sub.0.(θ/π).sup.1/3                  (25)

The above equations are valid if the cross-section of the chute 54 iscircular, with slot 54' having a constant gap, as shown in FIG. 7A.

However, it is quite possible to envisage (FIG. 7B) the chute 55 havinga semi-circular cross-section, a wall of the slot 55' extendedvertically upwards forming a lateral face 55" and the other 55"' beingrounded, in a semi-circle.

FIG. 7C shows a chute 56 in the shape of a droplet, i.e. having acircular cross-section truncated horizontally at the top 56' and havinga trapezoidal bottom section 56" which widens at the bottom, the smallbase of the trapezoid having the width of the gap (H) which extends thelatter downwards, and the two lateral faces 56"' and 56"" of the chutebeing symmetrical relative to a median vertical plane 56 and arcuate,for example.

The chute 58 (FIG. 7D) can also be in the shape of a semi-droplet withone face 58' extending the slot as in the case of FIG. 7B.

A cross-section of the chute 59, which is square or rectangular, (FIG.7E), with (or without) a lateral face 59' in the same plane as the wallsof the slot 59" is also possible, etc..

For these different shapes, it is then sufficient to define anequivalent hydraulic diameter: D_(E) =4S/P, thus an equivalent radiusR_(E), in which:

S=the surface area of the cross-section of the chute

P=the perimeter of the cross-section of the chute.

The chute can be calculated using the principle (2).

Assuming that the surface areas are equivalent, the geometric parametersof these shapes can also be calculated as a function of R(1).

Thus the combined decrease, relative to the horizontal die plate, of thecross-section of the distribution chute and the height of the slot,ensure that the material is distributed in a thoroughly homogeneousmanner in this area owing to the observance of the conditions ofpressure drop, compression time and shear velocity respectively suchthat they are substantially identical irrespective of the flow pathstaken by the material.

FIGS. 8A, 8B, 8C and 8D show schematically some examples of adistribution chamber according to embodiments of the invention which,being symmetrical relative to the vertical plane (120, 120', 120",120"') passing through axis of the feed duct (121, 121', 121", 121"')can thus have a generally cylindrical shape 122 as described above (FIG.8A), in sections of a circle 123, 124 which are not closed (FIGS. 8B and8C), or U-shaped 125, of which the base 126 is rounded to a greater orlesser extent (FIG. 8D).

Owing to the original shape proposed by the invention, which has a feedduct perpendicular to the spinning head and a distribution area relativeto this duct, the spinning extrusion head can assume shapes of thistype.

The lateral openings 126, 127, 128 respectively provided in the case ofthe embodiments, which are open to a greater or lesser extent,corresponding to FIGS. 8B, 8C and 8D, further enable fibers or threadsto be introduced laterally into the hollow punch in the head.

With reference to FIGS. 9A to 9C it can also be seen that the extrusionhead according to the invention can have a cylindrical body member 60with a hollow punch 61 and lateral feed 62.

The body member (FIG. 9B) can also be a section of a cylinder 63 whichis symmetrical relative to the vertical plane 64 passing through theaxis of the duct 67, with a central punch 65 and a lateral slot 66 inthe shape of a cylindrical ring section, for example with radial walls,located opposite the lateral duct 67 relative to the axis of the head.

Likewise, the extrusion head according to the invention can be producedin two body members or parts 68, 69, for example, which are semi-annularor in the form of a cylindrical (FIG. 9C) or oval ring section and whichcan be identical, for example. The polymer enters laterally via theopposite pipes 68' and 69' respectively.

The two semi-annular sections are disposed opposite one another but arenot in contact. Apart from the fact that it facilitates the passage ofthe fibers or threads in the extrusion head, this arrangement createsempty spaces in the sheet of filaments produced enabling other productsto be introduced into the assembly.

FIGS. 10A, 10B and 10C are further embodiments of the extrusion headaccording to the invention.

FIG. 10A shows an extrusion head 70 having four body members with across-section in the form of a quarter of a cylindrical ring 71, 72, 73,74 which are identical and fed by a feed duct or pipe 75, 76, 77, 78respectively. The chambers inside these bodies are of the type having achute and extension slot at the bottom of the chamber with a constantclearance, for example.

FIG. 10B shows a head having three identical body members in the form ofrectangular die plate bodies 80, 81, 82 disposed adjacent and at rightangles to one other and leaving a square central space 83 which is openat its side 84.

FIG. 10C shows four identical rectangular die plate bodies, for examplehaving a chamber of the type described in FIG. 11, one body member 85being disposed along the side 84 of the square 83.

The embodiment described more particularly in this case is in no waylimiting, as has been understood, and any other embodiment of thechamber, for example a chamber of the type shown in FIG. 11, fulfillingthe above criteria can be suitable.

FIG. 11 shows a chamber 90 which is supplied via a lateral pipe 91 atthe top 92 of the said chamber. The latter has a rectangular section forthe passage of the pasty material introduced at 92, but it can equallywell be trapezoidal, for example, and it decreases gradually in thedirection away from the horizontal plane passing through the lowergenerating line of the feed pipe.

With reference to FIG. 12 a method of using the extrusion head accordingto the invention more particularly described in this case, applied in anon-restrictive manner in the manufacture of extruded synthetic materialfilaments, will now be described.

The synthetic material, for example a thermoplastic polymer, e.g. apolyamide, is stored in the form of granules in a hopper 100 which feedsa vertical melting furnace 101. The polymer is melted in this furnaceand is then transported in the molten and pressurized state by ametering pump 102, for example a gear pump of which the role is toensure that the molten polymer is fed into the duct at a pressure anddelivery rate which are perfectly uniform.

It is perfectly possible to install upstream of this feed duct a staticmixer for example of which the function would be to improve further thehomogenizing of the temperature and velocity of the molten polymer.

The metering pump feeds the duct 103 which opens onto the extrusion head104 in a chamber fulfilling the conditions of the invention.

This head is heated for example by means 105 known per se which can beelectrical, for example.

At the pressure exerted, the polymer flows homogeneously into theinternal chamber up to the lower extrusion plate where the polymer overthe entire periphery of the head is of homogeneous viscosity.

The polymer then flows from the apertures in the spinning plate in theform of fluid jets 106 which are mechanically drawn then cooled in theform of a plurality of continuous filaments 107.

The annular extrusion head is provided with a central passage 108,through which a linear material, for example a continuous glass yarn109, is projected.

By extrusion then mechanical drawing after the head 104, a conical sheetis formed of which the tip faces downwards and which is guided towards acollection device provided with a notch 110, for example, which causesthe yarn and the sheet to join physically and produces a singlecomposite bundle. The bundle is then wound, for example, directly onto arotating support 111 on which it is distributed in a manner known per seby a notched plate 112 moved in a reciprocating manner illustratedschematically by the double arrow in FIG. 12.

One of the embodiments described above will be taken as an example. Thisis an extrusion head of the type illustrated by FIGS. 3A to 3D, 4, 5 and6.

This head has the following features:

diameter of feed duct (19): 20 mm

initial diameter of cylindrical: 20 mm chute (2R_(O))

external radius of slot (R_(e)): 88.5 mm

internal radius of slot (R_(i)): 84.5 mm

constant clearance of slot (H): 4 mm

maximum height of slot (Y₀): 157.5 mm

The variations in the diameter of the chute and the height of the slotare obtained by equations (24) and (25).

temperature of head body: 250° C.

head delivery rate: 20 kg/h

The material with which the head is supplied is a homopolymerpolypropylene of which the flow figure is 20 dg/min., measured accordingto ISO standard 1133.

The shearing rate of this material in the chute γ_(g) can vary about3.5. The shearing rate thereof in the slot γ_(f) likewise varies about3.8.

None of the areas in the head is supplied with an excess of or toolittle material. It is noted in particular that the temperature of thepolymer in a horizontal plane passing through the base of the slotvaries very little. This variation is of the order of 1° C. between thecentral core (approximately 240° C.) and the outer and inner edges ofthe slot (approximately 241° C.). The plate with which the base of thehead is provided is perforated with 768 apertures disposed over 8concentric circles. The diameter of these orifices is 550 μm and theirheight/diameter ratio is 4.

The filaments obtained have a highly uniform diameter in the region of25 μm.

As is self-evident and also results from the above, the presentinvention is not restricted to the embodiments described in particular.

We claim:
 1. Extrusion head (14, 70, 104) for producing continuousfilaments of uniform diameter from a material which has been heated toform a paste, comprising at least one body member (1, 16, 60, 63, 68,69, 71, 72, 73, 74, 80, 81, 82, 85) defining a vertically orienteddistribution chamber (4, 15), having a vertical height, for distributingpasty material above a plate (38) perforated with a plurality of rows ofspaced extrusion apertures (40), said chamber being supplied with saidpasty material via at least one upper lateral feed duct (5, 19, 62, 67,68', 75, 76, 77, 78, 103), extending about an axis (6, 20) with aterminal part thereof defining an inlet aperture (10, 21) connectingwith said chamber, characterized in that said distribution chamber (4,15) has a cross-section through which said pasty material passesdownwards and away from said lateral feed duct (5, 19) to define adirection of flow for said pasty material, which cross-section, over atleast part (24) of said height of the chamber, gradually decreases atincreasing distances (1) from said lateral feed duct (5, 19), asmeasured in a direction along said direction of flow of said pastymaterial, said distribution chamber having upper and lower sections, anddecreasing in size in accordance with the following formulae:

    R(1)=R.sub.0 (1/L).sup.1/3

    Y(1)=Y.sub.0 (1/L).sup.2/3

in which: R₀ =radius of said upper section at right angles to the axisof said feed duct at said inlet aperture; L=length of said lower sectionmeasured from the axis of said feed duct; Y₀ =Maximum height (Y) of saidlower section at right angles to the axis of said feed duct to createover time substantially identical pressure and shearing stresses on saidpasty material between said lateral feed duct (5, 19) and said bottom(27) of the chamber, respectively, irrespective of the path said pastymaterial takes when it flows from said lateral feed duct and out of saidbottom of said chamber.
 2. Extrusion head according to claim 1,characterized in that said chamber has a lower section (11, 31, 50) witha clearance (H) in the form of a slot having a vertical height (Y) whichdecreases gradually in said direction away from said lateral feed duct(5, 19).
 3. Extrusion head according to claim 2, characterized in thatsaid slot has cylindrical vertical lateral walls with a constantclearance (H) and a height (Y), relative to the plane (13, 27, 51)delimiting said bottom (27) of said chamber (4, 15) which graduallydecreases in said direction away from said lateral feed duct (5, 19). 4.Extrusion head according to claim 2, characterized in that said slot hascylindrical vertical lateral walls with a clearance (H) and a height (Y)relative to the plane delimiting said bottom of the chamber, both ofwhich decrease gradually in said direction away from said lateral feedduct.
 5. Extrusion head according to claim 2, characterized in that thechamber comprises an upper section (9, 28, 54, 55, 56, 58, 59) in theform of a chute of which the cross-section (s) decreases gradually insaid direction away from said lateral feed duct.
 6. Extrusion head forproducing continuous filaments from molten synthetic material comprisingat least one body member (1, 16, 60, 63, 68, 69, 71, 72, 73, 74, 80, 81,82, 85) defining an annular distribution chamber for distributing themolten synthetic material above a horizontal plate (38) perforated withextrusion apertures (40), said chamber having a bottom (27) and beingsupplied with synthetic material via a lateral feed duct disposed on oneside thereof and extending about an axis (6, 20) and having an inletaperture, characterized in that the chamber comprises:an annular uppersection (9, 28, 54, 55, 56, 58, 59) in the form of a chute extendingalong a chute axis and having a cross-section (s) which, as measuredalong said chute axis, decreases gradually in a direction away from saidinlet aperture (10, 21) of said lateral feed duct (5, 19, 62, 67, 68',75, 76, 77, 78, 103) which leads into said chamber to a minimumcross-section on the diametrically opposite side of said chamber; anannular lower section (11, 31, 50) disposed between said annular uppersection and said extrusion apertures and in communication with saidupper section and with said extrusion apertures (40) and havingcylindrical vertical lateral walls with a constant clearance (H) and aheight (Y) relative to the plane delimiting said bottom (27) of saidchamber which decreases gradually in said direction away from said inletaperture to a minimum cross-section on the diametrically opposite sideof said chamber, said distribution chamber decreasing in size inaccordance with the following formulae:

    R(1)=R.sub.0 (1/L).sup.1/3

    Y(1)=Y.sub.0 (1/L).sup.2/3

in which: R₀ =radius of said chute at right angles to the axis of saidfeed duct at said inlet aperture; L=length of said lower sectionmeasured from the axis of said feed duct; Y₀ =Maximum height (Y) of saidvertical lateral wall at right angles to the axis of said feed duct tocreate over time substantially identical pressure and shearing stresseson said pasty material between said lateral feed duct (5, 19) and saidbottom (27) of the chamber, respectively, irrespective of the path saidpasty material takes when it flows from said lateral feed duct and outof said bottom of said chamber.
 7. Extrusion head according to claims 5or 6, characterized in that said chute (54, 55) has one of a circularand semi-circular cross-section.
 8. Extrusion head according to claims 5or 6, characterized in that said chute (59) has one of a square andrectangular cross-section.
 9. Extrusion head according to claims 5 or 6,characterized in that said chute (56, 58) has a cross-section in theform of one of a droplet and semi-droplet.
 10. Extrusion head accordingto claims 1 or 6, characterized in that:R₀ =K. (H², L)^(1/3;) and Y₀=K'. (H², L)^(1/3), and K and K' being constants.
 11. Extrusion headaccording to claim 10, characterized in that K is substantially 0.607and K' is substantially 2.3398.
 12. Extrusion head according to claims 1or 6, characterized in that said distribution chamber includes twosections which are symmetrical relative to a vertical plane (8) passingthrough said axis of said feed duct.
 13. Extrusion head according toclaim 12, characterized in that said sections have a horizontal section,at said bottom of said chamber, of O-shaped configuration.
 14. Extrusionhead according to claim 12, characterized in that said sections have ahorizontal section, at said bottom of said chamber, of one of a C andU-shaped configuration.
 15. Extrusion head according to claims 1 or 6,characterized in that said distribution chamber comprises a plurality ofidentical body members (68, 69, 71, 72, 73, 74; 80, 81, 82, 85), eachsupplied via a lateral feed duct at the top thereof.
 16. Extrusion headaccording to claim 14, characterized in that said body members aredisposed about a central recess.
 17. Extrusion head (14) according toclaims 1 or 6, characterized in that said distribution chamber includesa central hollow cylindrical punch (3, 18).
 18. Extrusion head (14)according to claims 1 or 6, characterized in that a lower section (15)of said distribution chamber leads onto an annular extrusion chamber(34) having a constant cross-section in the form of an invertedtrapezoid.
 19. Extrusion head (14) according to claims 1 or 6,characterized in that a lower section (15) of said distribution chamberopens onto an annular extrusion chamber section which is equipped atsaid bottom of said distribution chamber with a plate (38) perforatedwith extrusion apertures and with a grid (36) disposed above said platefor homogenizing said pasty material before it is extruded through thesaid plate.
 20. Extrusion head according to claims 1 or 6, characterizedin that said distribution chamber includes heating cartridges (41, 42)associated with said body member.
 21. Extrusion head according to claims1 or 6, characterized in that said distribution chamber includes heatingmeans in at least two sections of said body member, so as to heat thesaid sections independently.